Kanna – Dai Prep

Kanna – Dai Prep

Thank you for visiting my blog. In this series I am preparing the kanna dai, or wooden body of a Japanese hand plane. The parts of a new plane are each individually made by craftsmen who specialize in a portion of the total process. The blacksmith’s task is to forge the blade. The smith will sometimes make the sub-blade or chip breaker. The blade is afforded a basic preparation by either the blacksmith himself, one of his staff, or a third party. Next the dai-ya makes the plane body to fit that blade and chip breaker. The dai-ya is so named because he cuts the dai, or plane body. Finally it is our job, as the end user, to complete the task of preparing the plane.

The dai-ya, using basic hand tools, quickly and accurately chop out the mortise and fit the blade. Dai-ya differ in their style much the same as blacksmiths and woodworkers each differ in their own style. I have worked with dai from dai-ya such as Inomoto-san and Nimura-san. I can see that each take different steps to arrive at their result. Each dai-ya chooses how much effort they will leave to the end user.

The first step is to fit the blade into the dai mortise. I begin the process by applying graphite to the back of the blade and mixing it with mineral oil.

Then I insert the blade into the kanna dai, tapping gently to seat it. Graphite rubs off onto the high spots revealing the contact areas.

The graphite shows that the center of the bed is high. What I want instead is for the blade to be fitted tightly at the sides and at the bottom of the bed. I prefer supporting the blade along the bevel and clamping the blade at the sides.

Next, I use a chisel to pare lightly at the high spots, then repeat the graphite procedure again. I repeat this process until the desired fit and pattern are revealed.

This is beginning to look exactly like what I want. At this stage I will reinsert the blade and determine which side is offering more resistance. I will then lightly pare away that side. My goal is to make the two sides equal so that the blade advances forward consistently when tapped.

Once I make good progress is made on that front, I next begin adjusting the sides to create a slight clearance. Making this clearance allows the blade to be adjusted side to side.

Once I establish a light clearance on both sides of the blade I can reinstall the blade.

Next I chamfer the leading inside edges of the osae-mizo (the side grooves) to prevent shavings from catching at the corners.

This dai has been easy work, the mouth and wear perfectly set right from Inomoto-san. For those unfamiliar, the ‘wear’ is the area of the dia immediately opposite the blade. As a shaving passes through the mouth it has the blade and chip breaker on one side and the wear on the opposing side. If the angle of the wear is too shallow the shaving will bind. If shavings bind rather than pass through the mouth unhindered, the first step is not to open the mouth, but to increase the clearance between the chip breaker and the wear. I do this by paring from the mouth toward the top of the plane, but without affecting the mouth opening.

I did not need to make clearance, but I’ve placed my chisel at the point at which one would need to make clearance.

In a western plane, with a properly set chip breaker, a tight mouth is somewhat unnecessary. In my experience with a kanna, however, I find a tight mouth more critical to the plane’s operation. An open mouth will allow the plane to snipe the end of the board, something that is quite undesirable on a finish plane.

The next step is to begin installing the chip breaker.

It is ideal for the cross pin to contact the chip breaker at the center of the chip breaker, and so I adjust the fit accordingly.

If the chip breaker is not even close I may have to examine the placement of the pin, then plug the current hole and move the pin. Or if the chip breaker doesn’t contact the pin at all, then it’s best to replace the pin with a larger size pin. However if they are both in contact but just too tight then I begin to make clearance.

These were contacting nicely, but initially I was getting contact across the full width of the chip breaker, I really only want contact in the center. I began to file the outside of the pin to create the additional clearance. A caveat being that filing the pin weakens it, however in this case the amount being filed is less than .010″, and Inomoto-san used a steel pin, so it’s quite sturdy.

I now show clearance on the sides and contact in the center.

The chip breaker is able to advanced with light taps from my brass hammer. I like the movement to be easy enough that advancing the chip breaker will not move the main blade, but not so loose that the shaving can push the chip breaker away from the edge.

I withdrawal the blades and move on to prepping the dai’s sole. Ideally a smoothing plane should make contact with the wood at two points, one point immediately ahead of the mouth and the other at the immediate rear of the plane.

The dai has been sitting for a few weeks to acclimatize to the local humidity level. The dai has not moved in that time which is encouraging.

Next I set 600 grit sandpaper onto the granite surface plate, and draw the plane toward myself in one movement. I do not rub back and forth as I want the sandpaper to remain taught.

Next, I continue to work the dai in this manner until there is contact across both points fully.

I then check for flatness with my straight edge to ensure that I have done work properly. The sole is now flat, but I must create clearance between the two contact points by scraping. The process of scraping requires another plane called the dai-naoshi-ganna, or bottom scraper plane.

The dai-naoshi-ganna, or dai-scraper, has a blade bedded at about 85 degrees.

The width of the contact points should be approximately 10mm of contact at the rear, and 6mm contact at the mouth. The dai-naoshi-ganna has 10mm of clearance between the edge of the blade and the side of the plane….perfect!

I scrape in the direction of the rays, as I point out here.

Now I can begin scraping, my first step is to clamp a piece of scrap maple at the end of the dai, which will allow the scraper to make a nice crisp line while utilizing the scraper’s built in clearance to create the exact width of contact that I desire.

I do not want a ledge, however, so I have cambered the blade on my scraper so that the cut feathers at the edges.

Ahead of the mouth, I want a smaller contact point. I created a fence which will allow me to adjust the contact point to be exactly what I’m looking for. I hold the fence in place as I scrape.

The installed blade will apply pressure to the wooden bed, this pressure will bulge the sole outward slightly which can lift the cutting edge off of the work. Inomoto-san has already taken care to scrape the area hollow.

My next step is to touch up the chamfers at the sides of the plane, they had some light tearout but I made sure to clean them up. I did this with a standard plane, as I do not have a 60 degree chamfer plane.

My final sole preparation is to burnish wax into the contact strips.

Next, I seal the end grain exposures on the plane with shellac with exception to the bed.

Finally I touch up the exterior surfaces to remove signs of handling. I use a chamfer plane and smoothing plane to complete this step.

And the result:

Next I set the blade. I sight down the sole of the plane looking for an even reveal of the protruding blade. I’m pointing out here the uneven protrusion, I will tap the blade along its side to even it out.

Next I install the chip breaker, I utilize light coming through the mouth and reflecting off of the main blade to determine how far my chip breaker is from the edge of the blade. I want a fairly tight setting and I will continue to adjust after beginning to cut shavings.

Now to test my result. Proper clearance is visible where needed.

To test the plane I use a wide piece of material, I want to see if any issues will arrive in normal use. The first shaving is a failure, showing that it has caught at the edges of the blade.

Not to worry, however, the reason for this is that I have not cut clearance at the mimi (ears) of the blade. The chip breaker should be wider than the shaving. I overlay the chip breaker, then mark the blade for trimming.

After some grinding at the edges.

And now I can try again. This time it is a success, having cut a full width shavings on Honduran mahogany. I’m aiming for thin shavings that shoot straight out of the plane. I adjust my chip breaker blindly at this point, tapping at the edges until the chip responds properly as it does here.

And most important, the resulting surface created on the wood.

Thank you for following along with this marathon of a post, I hope you have enjoyed. I want to again thank my many mentors. Please comment below!

Thank you for the detailed explanations. I became interested in Japanese tools about 2 years ago. I have several books, but I learned a few new things from your article (plus, your pictures are better than anything I’ve seen in my books).

You mentioned that you can get some snipe on your board if the mouth is left open too much. I have had this problem too, but I solved it by not carving the relief on the sides of the mouth. Now that I’m thinking about it, though, I think you can still carve the relief, but start the relieved area past the area where the blade is? I do all my operations by hand, so this really helps for my scrub plane and jointer plane.